The article by R. J. Chen et al. entitled “Molecular desorption from single-walled carbon nanotubes” published in Applied Physics Letters, Vol. 79, No. 14, 2258 (2001), states that powerful illumination in the ultraviolet or the visible can modify the electrical characteristics of a nanotube transistor by desorbing the oxygen molecules present on the electrodes. That phenomenon is fast, but in terms of reversibility, several tens of minutes are generally necessary to reestablish the initial current. That phenomenon which requires a large amount of power, is not wavelength specific and it is difficult to reverse.
The article by K. Balasubramanian et al. entitled “Photoelectronic transport imaging of individual semiconducting carbon nanotubes” published in Applied Physics Letters, Vol. 84, No. 13 (2004), states that photons having a wavelength situated at 514.5 nanometers (nm) and/or at 647.1 nm can generate a photo-current in a non-functionalized carbon nanotube transistor: the currents that are generated are very weak (<1 nanoamps (nA)) and can be detected only when the transistor is in the off state.
The article by Freitag et al. “Photoconductivity of single carbon nanotubes” published in Nano Letters, Vol. 3, No. 8, pp. 1067-1071 (2003), states that a nanotube transistor can be used to detect infrared photons. The current in a nanotube transistor can be modified by photons providing the wavelength of the light corresponds to the energy of one of the permitted transitions between Van Hove singularities (e.g. the forbidden band) of the semiconductive nanotube serving as a channel for the transistor. In general, this wavelength lies in the infrared for the first two accessible transitions. It is ultimately defined by the atomic structure of the nanotube (diameter and chirality).
The modifications that have been observed to the electrical characteristics of a transistor based on nanotubes by the presence of light are very small. Although they can be used to detect infrared radiation, the transistor is not genuinely “optically controlled”. Only its off state current varies, and only in very small amounts. Finally, the process used (direct creation of electron-hole pairs through the forbidden band of the non-functionalized nanotube) possesses very low quantum efficiency (of the order of 10−7).
The article by A. Star et al. entitled “Nanotube optoelectronic memory devices”, published in Nano Letters, June 2004, states that by functionalizing a device based on carbon nanotubes with a photosensitive polymer, it is possible to provide a memory function. For this purpose, a set of nanotubes is covered in a thick polymer film (drop deposited on the chip). That thus concerns polymers (very large molecules) being deposited in non-controlled manner in the form of very thick layers. When the device is illuminated, the Id(Vgs) electrical characteristic is shifted, thus indicating that electrons have been transferred to the polymer. When illumination is stopped, the device conserves its characteristics for a very long time (several minutes), thus providing a “memory” effect. That technique is limited to “memory” type characteristics and is not compatible with dense integration.
The article by Rotkin and Zmarov entitled “Nanotube light-controlled electronic switch” published in International Journal of Nanoscience, Vol. 1, Nos. 3 and 4 (2002), pp. 347-355 proposes displacing an electric charge in the proximity of a carbon nanotube by using a shape-changing molecule. When a photon is absorbed, the molecule deforms. According to that theoretical study, if the molecule carries a charge at its end further from the tube, then the charge can be moved mechanically towards or away from the tube, which can serve to modify the characteristics of the device. In any event, that technique requires shape-changing molecules to be used.